Do not look for version number on editable pip packages

[cgibb]

If the user has a local python site and installed editable packages,
they will appear in the output of pip freeze in a different format
than other installed packages.

Testing

Tested on Ubuntu as normal user with an editable copy of colcon-bundle installed. colcon bundle succeeds in my catkin workspace.

[murphm8]

Hmm, so does this mean that pip freeze is giving us the versions of all the packages installed into the local environment and the bundle?

[cgibb]

The python interpreter in the bundle is actually also pulling in the system pip module rather than the one in the bundle.

When running from my workspace:

$ ./bundle/bundle_staging/usr/bin/python3 -m pip --version
pip 19.0.3 from $HOME/.local/lib/python3.5/site-packages/pip (python 3.5)

So an alternative could be altering the python path configuration.

[murphm8]

Per our discussion: We should use the command line options to ignore the system paths when invoking Python.

[cgibb]

Fixed the formatting and merged in latest changes from /master.

I haven't figured out a way to ignore the system paths and still produce a proper bundle, so I think the solution here is what we should use for now (as system libraries haven't been causing any other problems that we know of).

[murphm8]

I filed #40 to follow up on the issues exposed in this PR.